Pedological and Isotopic Relations of a Highland Tropical Peatland,

Mountain Range of the Espinhaço Meridional (Brazil)

Ingrid Horák, Pablo Vidal-Torrado, Alexandre Christófaro Silva, and Luiz Carlos Ruiz Pessenda. 2011. Revista Brasil Ciencia Solo 35(1): 41-52.

Reviewed by: Paul DeckerSWS 5716: Environmental Pedology

April 20, 2015

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Research Motivations

• Peatland soils dominated by organic matter illustrate paleo-conditions• Climatic status of the past• Atmospheric carbon levels and implications for climate change• Vegetation trends over Earth’s history• Reconstructing the past from preserved soil materials

• Ecological interactions• Plant communities• Hydrology• Soil material and characteristics

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Goal of Research

• Histosols of peatlands behave as a record of temporal and spatial dynamics of vegetation.• What vegetation types grew back then?• Where did they grow?• Why did they grow?• How can this information be tied into the Earth in the present?

• Interactions of soil properties and pedological principles• Organic matter content• Fibric material; Oi, Oe, Oa

• Physical properties related to age and depth

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Study Area

• Histic peatlands of Pau-de-Fruta Special Protection Area

• Southern Espinhaço Mountains of Coastal Brazil

• Depressional mountain peatlands • 82 of total 1,700 ha (4.8%)• 1,300 – 1,400 m ASL• 143.7 cm annual rainfall• Cold, dry winters (June-Aug)• Mild, wet summers (Oct-Apr)• Mosaic of forest, grassland, and savanna

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Methodology

• Soil core extracted using a vibro-corer• Profile selected based on deepest available (505 cm)• 43 subsamples of the profile were taken at 10 cm intervals• Portions excluded due to water content (water table)

• Analytics include:• Bulk density (g cm-3), gravimetric water content, OM content, OM density,

mineralogy, Eh, pH, color, rubbed and unrubbed content

• 13 total horizons were described from profile• 10 were found to be Histic• O-C sequence, with OM underlain by sandy deposits.

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Results

• Base of profile contains unstructured gravel and sand

• Water layer with high viscosity OM from 60-137 cm

• Increased density and low hydraulic conductivity in lower layers; permanent anoxia

• Oldest material at bottom, younger with ascending depth

• Max sedimentation between 55 and 60 cm; 1.54 cm yr -

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• Varying degrees of decomposition with depth

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Results

• Lighter colors (10 YR 4/4) near surface with darker colors (10YR 2/1) near base

• Sapric (Oa) near base (202-475 cm)

• Hemic (Oe) from 40-187 cm

• Fibric (Oi) with 30 cm of surface• Decreased rubbed fiber content with

depth• Moisture content generally decreased

towards base• Related to density of soil and

moisture holding capacity• Evidence of soil profile collapse

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Results

• High C:N illustrate terrestrial plants

• Low C:N illustrate algae and phytoplankton

• C4 plants (grasses) increase, field vegetation increases

• Iron Age (very cold, very dry), added to field vegetation type

• Moisture fluctuations yield fluctuating values of C:N short, dry periods, charcoal and sandy material found

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Implications and Conclusions

• Degree of decomposition with depth• Law of Superposition • C:N illustrates proportion of woody

versus grassy vegetation type• Humidity and temperature of time

period• Indicates fluctuation of climate,

temperature, and moisture of study site with time

• Evidence of interaction between soil genesis and soil forming factors• Vegetation• Climate• Time

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Pedological Principles

• Soil forming factors• Necessity of time for OM accumulation• Parent material linked to vegetation type• Topographic effects from Depressional position• Vegetation effects on OM type, and consistence• Climate variability and links to soil profile

• New example from organic soil type• Variations of morphology assessment• Principles surrounding Histosol soil order• Taxonomic class of this study profile:

• Sandy, siliceous, dysic, isothermic, Hemic Haplosaprists1

Courtesy: NRCS

1USDA, NRCS Keys to Soil Taxonomy